The present invention relates to the field of dentistry, and more particularly concerns prostheses of the fixed or connected type, such as bridges, crownwork, false stumps, implants or removal/nonremovable dentures.
For economic reasons, it has most often been proposed to produce dental prostheses from a precious, semiprecious or nonprecious metal alloy, such as from nickel-chromium alloy or cobalt-based alloy.
For obvious aesthetic reasons, the design of such a prosthesis, which was purely of metallic nature, has developed to involve the manufacture of a cap which is still of metallic structure but is covered by a ceramic crown. The cap has a profile tailored to the implantation zone of the human body. The profile of the cap is produced on the basis of an impression of the implantation zone.
It is clear that there are a number of drawbacks with the manufacture of such prostheses, in particular because of the extent of work inside the mouth, significant production delays, high labour cost, misunderstandings between the dentist and the technician and a need for a plurality of operations in the mouth, which are time-consuming and uncomfortable for the patient.
In order to overcome the drawbacks mentioned above, solutions have been envisaged in the prior art with the aim of automating the manufacture of such prostheses.
Document EP-A-643 948 relates to a process for producing a dental prosthesis comprising a cap and a crown. The cap comprises an internal surface which is duplicate of the shape of the stump to be fitted out, and an external surface which is a mathematical enlargement of the surface of the stump.
The document FR-A-2 536 654 has thus described a process for producing a dental prosthesis consisting, in a first stage, in recording the shape of the implantation zone using an impression, microsensor or optical impression then, in a second stage, in automatically machining the prosthetic article while taking into account the recorded data and information provided by processing software. According to a first alternative embodiment, it is proposed to machine, on the one hand, the internal face of the cap to the shape of the implantation zone and the external face of the crown as a function of the envelope and the bite. The cap and the crown are selected from a supply of crowns and caps which are paired so that the external face of the cap has the same profile as the internal face of the crown.
This document describes, in particular, a second alternative embodiment which consists, on the basis of a recording of the shapes taken in the mouth, in machining the internal and external faces of the metal cap in a metal block, in taking a new recording of the external face of the metal crownwork, in machining the internal face of the crown as a function of this and from a ceramic block, then, as a function of the envelope and the bite, in machining the external face of it before assembling the metal cap with the ceramic crown.
Although such a document describes a process for automatic production of a dental prosthesis, it is apparent that there are drawbacks with the practical implementation of such a process. It should firstly be pointed out that, according to its first alternative embodiment, such a process requires the provision of a supply of crowns and caps to be paired, the number of which may be relatively high in order to try to cover all the prostheses configurations to be produced. However, it proves impossible in practice to provide a supply of prostheses matching all the morphologies of implantation zones. Furthermore, the second alternative embodiment requires the use of a plurality of manufacturing operations.
More fundamentally, it should be pointed out that the metal cap is generally produced homothetically with the implantation zone, whereas the crown has an external surface matched to the envelope of the buccal environment. The Applicant Company has pointed out that such an approach led in certain cases to the production of crowns having localized zones of reduced strength, the presence of which unequivocally affects the reliability of the prostheses produced in this way. In addition, this technique sometimes leads to obtaining unaesthetic prostheses, because of the fact that it is impossible, at least locally, to produce the crown in ceramic. There is therefore an apparent need to provide a manufacturing method designed, on the one hand, to take into account the clinical situation of the tooth to be fitted out and, on the other hand, to comply with the rules of aesthetics and the criteria of mechanical durability which ceramic crowns need to satisfy in order to provide long-term reliability.
The object of the invention is therefore to provide a process for producing a dental prosthesis, designed to make it possible to define the profile of the cap and of a crown while respectively taking account of the implantation zone and the environment of the prosthesis, while guaranteeing optimization of the profile of the cap in order to guarantee compliance with the criteria of mechanical durability and aesthetics of the crown.
To achieve this object, the process according to the invention is designed to allow the production of a dental prosthesis having at least, on the one hand, a prosthetic cap intended to be fitted on an implantation zone of the human body and, on the other hand, a prosthetic crown supported by the cap.
According to the invention, the process comprising:
defining a three-dimensional representation of the internal surface of the prosthesis, corresponding to the internal surface of the cap defined on the basis of the digitized three-dimensional representation of the implantation zone, while taking account of the rules connected with the insertion and sealing of a prosthesis,
defining a digitized three-dimensional representation of the external surface of the prosthesis, on the basis of the environmental parameters of the prosthesis while taking account of the constraints resulting from the internal surface of the prosthesis, consisting of the internal surface of the cap and of the digitized three-dimensional representation of the internal surface of the prosthesis,
and in defining a digitized three-dimensional representation of the external surface of the cap, on the basis of the external surface of the prosthesis, while taking account of the internal surface of the prosthesis, the criteria pertaining to mechanical durability in particular thickness, and aesthetic criteria.
The process according to the invention therefore has the advantage of making it possible to define a cap while taking into account the anatomical profile of the implantation zone, the external surface of the crown and production criteria for the crown, with a view to obtaining a prosthesis which is reliable in the long term. The subject of the invention also has the advantage of making it possible to determine, without requiring the manufacture of a prosthesis and on the basis of clinical information, whether it is possible to produce the cap and the crown under acceptable conditions of reliability and aesthetics. Such a process thus provides the possibility of choosing and adapting the profile of the cap as a function of the production conditions for the crown.